Last week, in Part 1 of this article, author Jason Norcross talked about the different ways commonly used to determine if you’re more pork than loin, if you catch our drift. Unfortunately, most of the methods usually used to determine body fat are woefully inadequate and rife with potential problems.
If you really want to know how much fat you’re packin’, the tried-and-true skinfold measurement is the way to go.
Here’s everything you ever wanted to know about skinfold measurements.
Skinfold Measurement – The Method of Choice
Skinfold measurements are probably one of the most misunderstood body composition methods. It’s true that most skinfold body fat equations have been derived by those used for HW (hydrostatic weighing), but unlike HW, which is markedly affected by day to day fluctuations in hydration, skinfold measurements of %BF aren’t nearly as affected by hydration. Skinfold calipers are also inexpensive. There are several different models available for less than $60 and a couple of different models that will run you $20. Both the Accu-Measure™ and Slim-Guide® cost about $20 and will do the trick for most people. Pictured below are the reference grade Harpenden calipers (black model) and the white plastic Accu-Measure™ calipers.
Skinfold measurements can be done by yourself using a 3-site method or with assistance from someone else using a 7-site method, although women will have to have a partner to do both the 3 and 7-site methods. (Women can get the thigh and suprailiac measurement by themselves, but it’s pretty tough for them to get a good tricep measurement by themselves. It’s possible with some calipers like the Fat-Track, but with most calipers, it’s very difficult. Inclusion of the triceps measurement is pretty important, too, as many women store a fair amount of fat there. )
Anyhow, after you practice a bit, you’ll find that your measurement technique will get pretty good. You won’t have a lot of variability if you’re only measuring yourself or someone else.
Unfortunately, once you take the measurements, you’ll have to plug the numbers into equations. Even though I recommend you use either one of two different equations, there are actually hundreds of equations, so feel free to use another one if you like. I’ll present the equations later on, but in the meantime, just remember a few things:
1. More sites = better reliability and less variability
2. More samples per site (3 is minimum) = better reliability and less variability
3. Practice makes perfect. For the first week or two, measure yourself or your partner every single day or until your day to day %BF values don’t vary more than 1%. You might think that the standard error of measurement is about 4%, but remember that you’re only measuring one person (yourself or your partner) and in my opinion, you should be able to replicate that measurement with little variation.
4. Measure yourself every week and preferably on the same day and at the same time. One week may not be enough to see a change, but being able to make a graph that plots 52 measurements over a year will clearly show you the picture.
5. Finally, the leaner you are, the more reliable skinfold measurements become. Any measure over 20mm is subject to a lot of variability. If you keep seeing several of these high measurements, then fat loss needs to become a priority right away.
1. All measurements should be made on the same side of the body. While it probably doesn’t matter all that much, small differences may occur between opposite sides of the body.
2. The calipers should be placed 1/2 inch below where you pinch the thumb and finger, perpendicular to the skinfold and halfway between the crest and base (the part that is closest to your fingertips is the base and the part that is closest to your hand is the crest).
3. The pinch should be maintained while reading the caliper (unless using a model like the Accu-Measure™ where you read the number after you hear it click).
4. Wait 1-2 seconds (no longer) to take and read the measurement.
5. Rotate through the different sites to give the skin adequate time to return to normal. (This one’s very important because it forces you to also learn the anatomical landmarks for skinfold measurement.)
6. Take a minimum of 3 measurements at each site and average the measurements; then add the averages together and plug them into the equations presented later on in this article.
1. Abdominal: vertical fold, 1-inch to the right of the umbilicus.
This one is very straightforward. You can have someone measure it for you (left picture) or you can do it yourself (right picture). One thing to note is the different hand position when you do it yourself. The key is to measure the same point each time so stay in line with the umbilicus.
2. Triceps: vertical fold, posterior midline of upper arm, halfway between the olecranon (elbow) and the acromion processes (bony point on top of the shoulder).
Using your hands as a measurement tool, find the midpoint of the triceps. Spread your thumb and middle finger from both hands to the maximum distance. Lock one of the digits on the top and bottom anatomical landmarks. Then bring them together in the middle of the triceps to find the skinfold site. Mark that site and have the person flex their triceps. By flexing, the subject separates the muscle from the fat. This isn’t usually a problem for most well-conditioned men and women, but it’s a nice trick to know anyway. As the person relaxes their triceps, grab the skinfold and take the measurement.
3. Chest (men): diagonal fold, halfway between the anterior axillary line (on the front of the body at the point where the arm inserts into the torso) and the nipple.
There isn’t much to explain here other than to make sure you’re on the lateral aspect of the pectoral muscle. These pictures show me using both types of calipers. This will probably be the toughest measurement to do on yourself, so here’s a tip: If you’re right handed, grab the skinfold of your left pectoral with your left hand and take the measurement with your right.
4. Chest (women): diagonal fold, 1/3 of the distance from the anterior axillary line to the nipple
5. Midaxillary: vertical fold, on the midaxillary line (a vertical line descending directly from the center of the armpit) at the level of the xiphoid process (the bony nub at the bottom of the sternum)
The “X” on the chest is the xiphoid process and the other “X” is the junction of the mid-axillary line with the horizontal line coming from the xiphoid process. It’s helpful to have your subject place his arm on top of his head while taking this measurement.
6. Subscapula: diagonal fold, 1/2 to 1-inch below and in line with the inferior (lower, inside) angle of the scapula.
The longer line marks the inside edge of the scapula. The other line is drawn to demonstrate where the bottom tip of the scapula is. This one’s also pretty straightforward. Just don’t try to do this one by yourself; it’s virtually impossible unless you’re a hyperflexible circus freak.
7. Suprailiac: diagonal fold, in line with the natural angle of the iliac crest (hip), just above the the iliac crest at the anterior axillary line (an imaginary line down the front of the body from where the arm inserts into the torso).
The “X” marks the anterior superior iliac spine (ASIS) and can easily be found. Just feel for the bony prominence near the front of the pelvis. You should feel it just before the pelvis begins to slope upward (as demonstrated by the line in the first picture). Find the anterior axillary line, grab and measure the fold right above the pelvic line. Be careful with this one. The closer you are to the ASIS, the smaller the measurement, but as you travel along the pelvic line, the folds will only get bigger. Just try for utmost consistency from week to week.
8. Thigh: vertical fold, on the anterior (front) midline of the thigh, half the distance between the proximal (nearest to body) aspect of the patella and the inguinal crease (line where leg inserts into trunk)
It helps to have the subject rest the foot of the leg being measured on a box, chair, or Smith machine bar. (See, the Smith Machine does have some utility!) Once you find the vertical midpoint, make sure that you’re even from a horizontal standpoint and not shifted medially or laterally. You can have the subject push down with the elevated foot to separate muscle from fat and then grab the fold and measure it.
Other Skinfold Observations
Skinfold measurements change primarily when there is a change in skinfold thickness (i.e., you gain or lose fat). A minor problem to watch for is dehydration, because this will decrease skinfold thickness also. You can minimize this potential for error by measuring in a hydrated state and by measuring at the same time of day each week.
Another advantage of skinfolds is the tangible feeling of grabbing on to your body fat, which you don’t get with any of the other methods. Finally, skinfold calipers are also cheaper, readily available and more convenient. For instance, try scheduling a weekly or even monthly appointment with the same tester at the same time of day for HW or Bod Pod! It’ll take a lot of effort and financially it would add up very quickly. That’s money better used on good food and supplements.
Skinfold Equations (Jackson-Pollack method)
Don’t worry. If you’re mathematically challenged, go to this great site to have all your calculations done for you: www.enforcergraphics.f2s.com/bodyfat.htm However, if you’re a “hands-on” guy, here are the equations:
NOTES: SUMS refers to the sum of the average skinfold thickness (mm) of the prescribed skinfold sites. Db refers to body density.
Male 3-Site Equation (SUM3 = chest, abdomen, thigh)
Db = 1.10938 – (0.0008267 * SUM3) + (0.0000016 * SUM32) – (0.000257 * AGE)
%BF = [(4.57/ Db) – 4.142] * 100
Male 7-Site Equation (SUM7 = chest, midaxillary, tricep, subscapula, abdomen, suprailiac, thigh)
Db = 1.112 – (0.00043499 * SUM7) + (0.00000055 * SUM72 ) – (0.00028826 * AGE)
%BF = [(4.57/ Db) – 4.142] * 100
Female 3-Site Equation (SUM3 = tricep, suprailiac, thigh)
Db = 1.0994921 – (0.0009929 * SUM3) + (0.0000023 * SUM32) – (0.0001392 * AGE)
%BF = [(4.57/ Db) – 4.142] * 100
Female 7-Site Equation (SUM7 = chest, midaxillary, tricep, subscapula, abdomen, suprailiac, thigh)
Db = 1.097 – (0.00046971 * SUM7) + (0.00000056 * SUM72 ) – (0.00012828 * AGE)
%BF = [(4.57/ Db) – 4.142] * 100
Why is age included in these formulas? As normal people (not T-mag readers!) age, there’s an increase in intra-abdominal fat, a decrease in total muscle mass, and a decrease in bone density (12). These equations try to account for these changes by adding body fat as we age. Of course, this doesn’t apply nearly as much to people who train with weights. Anyhow, whether you choose to put your actual age or choose to call yourself a 20-year old is up to you. Personally, I think anybody who trains hard with weights would do better to plug 20 in as their age, as it more accurately reflects your true muscle mass.
Let me put it this way: if your sum of seven skinfolds was 50mm when you were 25 and is still 50mm now that you’re 35, then I’m pretty confident that your body fat hasn’t increased markedly. You could still use 25 years in the equation. I suggest that you use the age at which you started to seriously train. Once again, it’s up to you, just be consistent with what you do.
In conclusion, most methods are expensive, inconvenient, unreliable and don’t improve on the accuracy of skinfolds. Skinfolds allow you to track your body composition as often as you want without burning a hole in your wallet. Just remember to pick one skinfold equation and stick with it. If that doesn’t suit you for some reason, pick up a higher end Tanita™ bioimpedance scale and follow my recommendations form part 1 of this article. Finally, don’t ever go back and forth between methods unless you want frustration and bad data.
Good luck and happy measuring!
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